Label-free Fluorescent Sensor for Detection of Single-stranded Nucleic Acids Based on G-rich Sequence

G -rich sequences with specific conformations (e.g. G-quadruplex and G -triplex) can interact with fluorescent dyes to enhance their fluorescence signal intensity, and are widely used for label -free fluorescent biosensing. In this study, two label -free fluorescent sensors based on G -rich sequences were constructed for detection of the gene sequence of a-amyloid protein (Aa), a marker of Alzheimer & PRIME;s syndrome, using thiosemicarbazone T (ThT) as the fluorescent dye. The experimental results showed that the G -rich sequences were present as G -triplexes when the length of the hairpin stem was 4 base pairs, and the output signal of the G -triplex sensor decreased with increasing concentration of Aa gene, with a linear detection range of 1-100 nmol/L and a detection limit of 0.3 nmol/L (S/N = 3). When the length of the hairpin stem was 8 base pairs and the base AATT was added at the 5 & PRIME; end, the G -rich signal decreased with the concentration of Aa gene. The G -rich sequences were mostly present as G-quadruplexes after binding to Aa gene, and the output signal of the G-quadruplex sensor was enhanced with increasing concentration of Aa gene, with a linear detection range of 0.1-100 nmol/L and a detection limit of 0.04 nmol/L (S/N = 3). The two sensors were prepared in a similar process but with different detection principles, providing a basis for further research and application of G -rich sequences. It also provided a new idea for the label -free fluorescence detection of single -stranded nucleic acids.